Topic on Extension talk:Semantic Forms Select/Flow

If I have the following code for a Semantic Forms Select:

{{{field
|ActionItemRequestorIs
|input type=SF_Select
|query=((Category:User));format~list;sep~,;link~none;headers~hide;limit~500
}}}

How can I set one of the results as a default for a new page created by that form.

In other words, what should I provide in place of "{{mydefaultvalue}}" in the code below (which does not work):

{{{field
|ActionItemRequestorIs
|input type=SF_Select
|query=((Category:User));format~list;sep~,;link~none;headers~hide;limit~500
|default={{mydefaultvalue}}
}}}

Same question